The present invention relates in general to substrate manufacturing technologies and in particular to apparatus and methods for the detection of an arc in a plasma processing system.
In the processing of a substrate, e.g., a semiconductor substrate or a glass panel such as one used in flat panel display manufacturing, plasma is often employed. The semiconductor or glass substrate is processed in a series of steps in which materials are deposited and materials are selectively removed using plasma processes A layer of particular material is deposited on the substrate, often using plasma to enhance the deposition process. Subsequently, the layer is patterned with a polymer mask using photolithography. The substrate is then placed in a plasma processing chamber on a substrate support structure comprising a mono-polar or bi-polar electrode, called a chuck or pedestal. Appropriate etchant gases then flow into the chamber and energized to form a plasma to etch exposed areas of the substrate.
Integrated circuits manufactured by these plasma processes now incorporate feature sizes as small as 100 nm, and as many as seven layers of material that is alternately deposited and patterned with these small features. The high density of components in these advanced integrated circuits increases the risk of dielectric breakdown and arcing between the components, or between the components and the plasma during plasma processing. Plasma arcs are generally caused by low plasma impedance which results in a steadily increasing current flow. If the resistance is low enough, the current will increase indefinitely (limited only by the power supply and impedance), creating a short circuit in which all energy transfer takes place. This may result in damage to the substrate as well as the plasma chamber. Often, the occurrence of an arc event is easy to determine since it measurably affects plasma process parameters, such as RF power or emission spectroscopy.
However, an arc can occur that neither consumes enough energy nor exists for a sufficient length of time to generate a distinguishable signal from the background plasma process noise (e.g., signal-to-noise ratio). These “micro-arcs” are more likely on the high-density multi-level circuits currently being manufactured. Such arcing can still cause failure of the circuit being manufactured and collateral damage to other circuits and portions of the substrate.
For example, the RF power used to sustain a plasma processing system is on the order of kilowatts; however, a small arc event on the substrate being processed can be on the order of watts. Subsequently, the arc event may be masked by normal multi-watt fluctuations in the plasma processing. Likewise, the small perturbation of the plasma light intensity due to the arc is less than the normal intensity fluctuations in the plasma; hence, spectroscopic detection of the arc also has poor signal-to-noise ratio. On the other hand, even a micro-arc generally has enough power density to effect a miniature explosion on the substrate. The vaporization of material creates vibrations in the substrate.
Unfortunately, the method often used to determine the extent of damage caused by an arc event, or if in fact an arc event actually occurred, is visually inspecting the surface of the substrate outside of the plasma chamber. Since the inspection cannot be done in-situ, it is generally performed only after a batch of substrates has been processed. At later stages of manufacturing, after a substantial amount of resources has been invested in each substrate, scraping an entire batch can be particularly costly, often on the order of several hundred thousand dollars.
In view of the foregoing, there are desired improved apparatus and methods for the detection of an arc in a plasma processing system.